1. Field of the Invention
The present invention relates to a servo pattern writing method for magnetic disk drives and to a magnetic disk drive. More particularly, the present invention is concerned with a servo pattern writing method for magnetic disk drives making it possible to readily write a high-density and easily controllable servo pattern, and a magnetic disk drive in which a servo pattern is written in this way.
2. Description of the Related Art
A magnetic disk drive (hereinafter simply a disk drive) is an apparatus that stores data by recording a magnetic pattern on a magnetic disk (hereinafter simply a disk) using a magnetic head (hereinafter simply a head), and that reads data by detecting a change in magnetic field caused by the recorded magnetic pattern. For specifying a position at which storing and reading are carried out, magnetic guides referred to as tracks are recorded on disks concentrically with the center of rotation of the disks as a center. By specifying a track, a position in a radial direction is defined. Each track is segmented in a circumferential direction into a plurality of portions referred to as sectors. Sector numbers indicating the numbers of sectors are recorded magnetically on each disk. Storing data is carried out in units of a sector. A position in the circumferential direction is defined by specifying a sector number.
In recent years, magnetic disk drives have had storage capacities thereof increased by improving the recording density in a circumferential direction and the recording density in a direction of tracks. For improving the recording density in the direction of tracks, servo information used to position a head is embedded discretely among data items on each medium for the purpose of recording. This recording method has become mainstream nowadays, and is generally termed an embedded servo method. Herein, the term is adopted. The embedded servo method makes it necessary to write all servo information on data surfaces in advance.
In a known disk drive, after disks are attached to an axis of rotation of a spindle motor 15, a servo track writer (STW) is used to write servo information on record surfaces. The servo track writer gives control so that while the position of each arm is being measured accurately by a laser measuring device, the arm is moved to a given position, and then given servo information (a servo pattern) is written. When writing a servo pattern is completed, the disk drive is dismounted from the STW, provided with a housing, and then sealed up. Thus, a complete disk drive is produced. The time required for writing a servo pattern is proportional to the number of tracks. When the number of tracks increases due to an improvement in track density, the time required for writing a servo pattern increases accordingly. Moreover, since writing a servo pattern is carried out for each surface of a disk by changing a head for applying a writing signal from one to another, if the number of disks gets larger, the total time required for writing servo patterns increases accordingly. The STW employs a laser measuring device and can therefore precisely control positioning. However, the STW is complex and expensive. Furthermore, writing a servo pattern must be carried out with the cover of a magnetic disk drive removed and with surfaces of disks exposed, and therefore must be achieved in a clean room. Thus, when the STW is used to write servo patterns, a dedicated facility and environment are needed.
As mentioned above, after a magnetic disk drive is mounted in an STW, a spindle motor in the disk drive is rotated, and a head in the disk drive is used to write servo patterns. However, the position of each arm is measured precisely by a laser measuring device and controlled to coincide with a given position. Tracks on which a servo pattern is thus written are not completely round because of vibrations of heads and disks during writing, or eccentricity or deflection of a spindle motor, but appear to vibrate relative to circular trajectories. For improving the recording density of the disk drive, it is required to reduce the spacing between tracks and thus increase the number of tracks that can be recorded on each disk. However, if tracks vibrate, adjoining tracks may interfere with each other. The spacing between tracks cannot therefore be narrowed very much. Consequently, the recording density cannot be improved. For improving the density of tracks, a servo pattern serving as a reference must be written very precisely. If the magnetic disk drive is mounted in the STW in order to write servo patterns, tracks cannot be written with sufficient precision for the aforesaid reasons.
Conceivably, an STW having a dedicated high-precision spindle motor and a dedicated actuator is prepared, and disks are attached to the STW in order to write servo patterns highly precisely, and then incorporated in a disk drive. In this way, servo patterns can be written very precisely, and eventually the density of tracks can be improved. However, since a plurality of disks are incorporated in a magnetic disk drive, if the disks have servo patterns written externally and are then incorporated, the servo pattern on each surface of disks becomes eccentric because of an error deriving from incorporation. Moreover, the magnitude and direction of eccentricity differ from surface to surface. As mentioned previously, an actuator in the magnetic disk drive is shared by disks, and heads associated with the disks are moved all together by the actuator. When a surface of disks to be accessed is changed from one to another, a head for applying or extracting a signal is changed from one to another. Consequently, if the magnitude and direction of eccentricity differ from surface to surface, there arises a problem that control to be given for changing a surface of disks to be accessed from one to another becomes complex, and the time required for access gets longer.
As described above, a dedicated facility and environment such as a clean room are required for writing a servo pattern using an STW. This poses a problem that if the work time in the clean room increases, production deteriorates. This problem becomes significant especially when the density of tracks is increased in order to improve recording density or the number of disks is increased in order to improve a storage capacity, because the work time increases accordingly.
As mentioned above, when a magnetic disk drive is mounted in an STW in order to write servo patterns, there arises a problem that the precision of the servo patterns is unsatisfactory. The method for solving this problem in which after a servo pattern is written on disks, the disks are incorporated in a disk drive has a problem that a difference in eccentricity among the incorporated disks leads to complex control and a longer time required for access.